The present invention relates to a light coupling element with a surface comprised of a material which is transparent to light of a given wavelength, wherein in at least one region of the surface a line grating is present with equidistant parallel line-form indentations or with equidistant parallel line-form elevations.
The present invention builds primarily on findings which were obtained on light coupling elements of said type to demonstrate chemical or biochemical reactions in conjunction with fluorescence. In this respect reference is made in particular to WO 01/02839, wherein within the scope of an analysis platform such a light coupling element is described. An effect, known as “abnormal reflection” is utilized. Therein a support provided with a layer is provided. This support, and also the layer, is preferably transparent to light of a given wavelength λ in the UV VIS or NIR range (200 nm to 2000 nm) of a light source, preferably of an at least approximately monochromatic light source, such as for example of a laser or an LED. In the case of dielectric material, the material of the layer has a substantially higher refractive index than the material of the support, viewed at the given wavelength. The surface of the support, on which the layer is placed, has a line grating, whose structure is transferred via the thin layer to the surface of the layer. In the utilized “abnormal reflection effect” light of the given wavelength is virtually completely reflected when a specific angle of incidence is maintained and virtually no light is transmitted along the layer or through the layer. With suitable selection of the structure parameters the evanescent, i.e. transversely damped, electromagnetic field in the immediate vicinity of the layer surface becomes especially strong, whereby fluorescence molecules are especially efficiently excited in this region. This permits detecting substantially lower concentrations of substances provided with so-called fluorescence labels at the layer surface of samples to be analyzed than was possible with methods known prior to that publication.
The line grating or the line gratings present at the two interfaces support substrate/layer and layer/ambient atmosphere, which in a view from above are aligned such that they are congruent one beneath the other are therein directed in the sense that the line-form indentations and the elevations resulting in between extend wavelike in one direction. Viewed as a structure wave, the light coupling element provided with the line gratings extends one-dimensionally perpendicular to the line-form indentations or elevations disposed in between. Taking into consideration this directionality, in view of the advance described in detail in that publication, laser light of said given wavelength is first polarized in a specific direction by means of a polarizer, before the platform with the light coupling element is impinged upon therewith.
If light coupling elements are considered for other optical analytical methods or for telecommunication purposes, thus for example for coupling in or respectively coupling out laser light into or, respectively from light wave-guiding layers, it is apparent even in these cases that the provided line gratings in said sense are directed one-dimensionally, i.e. the provided line-form indentations and elevations formed between them, extend in a direction along the surface. Due to this directionality in principle vectorial parameters of the light supplied to the light coupling element are spatially weighted and, depending on their direction, are affected differently by the light coupling element. Typically, when employing the advance according to the cited WO 01/02839, the impinging light is affected differently at the light coupling element depending on the direction of polarization.
It is the task of the present invention to provide a light coupling element of the above type, which in principle impinges to an increased extent upon vectorial parameters of the impinging light, such as in particular on its polarization, independently of the vector direction.
This is attained in a light coupling element of the above type, which has in at least one region of the surface equidistantly parallel line-form indentations, thereby that on the surface further equidistantly parallel line-form indentations are present, which intersect said first mentioned indentations.
Alternatively, this is attained on a light coupling element of the above type, in which in at least one region of the surface equidistantly parallel, line-form elevations are present, thereby that on said surface further equidistantly parallel line-form elevations are present, which intersect the first mentioned elevations.
The periodicity of the prior known as well as also the inventive gratings, i.e. the sequential distance of said indentations or elevations, is laid out as a function of the given wavelength of the light which is to be employed for the application purpose of the light coupling element.
Consequently, WO 01/02839 as well as also WO 00/75644 therefore proposes that if the light coupling element is to be applied with light of two wavelengths, to develop it with parallel indentations or elevations, but not with equidistant ones, i.e. with locally modulated grating periods or with intersecting line gratings, of which one is optimized with a first period for light of the one wavelength and whereon the second line grating, optimized for a second wavelength, is realized with a period deviating from the first.
Still vectorial parameters of the light of one of said wavelengths are treated therein and at the light coupling element with different weighting as a function of the vector direction, such as in particular depending on its direction of polarization.
In the light coupling element according to the invention, in which line-form indentations, which are equidistant and parallel to one another, intersect, islands of elevations are generated framed by said indentations and lying between them. Analogously, in the light coupling element of the above type, in which equidistantly parallel line-form elevations intersect, interspaced indentation islands are formed.
In connection with providing raised structures, reference can further be made to EP 1 040 874. Therein is proposed that in order to specifically affect the wettability of surfaces for optical analytical techniques, to develop surface areas, which are not to be wetted, with elevations structures, whose height does not fall below a certain minimum measure, namely of 50 nm to 10 μm such that regions provided with such structures in connection with the surface energy of the nonstructured surface material prevent wetting and that this wetting is concentrated in non-structured surface regions. Even though said structured regions according to EP 1 040 874 are not light coupling regions—since samples are precisely not to be present there—and the described raised structures do not have to satisfy any criteria with respect to optical effect, according to the present invention and as will yet be described, the field of surface wettability related to the surface energy of surface regions will also be addressed.
As stated, from the cited EP 1 040 874 the rules are known to define regions on a surface which are not to be wetted with hydrophobically structured surfaces and therewith also those to be wetted. In the approach according to the present invention the following advantages are accomplished in this connection in addition to the solution of the above described task:
The surface energy of an interface with a liquid is proportional to the surface available in a defined observation region. If the surface in said region is planar, this surface which can be denoted as specific surface, is far smaller than if in the same observation region the surface is roughened. If on such a surface region a drop of liquid is deposited, it expands on this region such that an energy minimum is attained. This means, pragmatically that a drop of liquid on said region with increasing specific surface increasingly contracts until the effect is reached utilized according to EP 1 040 874, that namely the liquid drops off the observed region.